Membranes Chapter 5 Copyright © McGraw-Hill Companies Permission required for reproduction or display

Cell Membrane Proteins Diffusion Facilitated Diffusion Osmosis Outline Phospholipid Bilayer Fluid Mosaic Model Cell Membrane Proteins Diffusion Facilitated Diffusion Osmosis Bulk Transport Active Transport Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Degree of fluidity determined by degree of alignment. Phospholipid Bilayer Phospholipids have a glycerol backbone with two attached fatty acid chains. One end is nonpolar (water-insoluble) while other end is polar (water-soluble). When placed in water, polar ends seek partners for hydrogen bonding, and nonpolar tails pack together. Lipid bilayer formed. Degree of fluidity determined by degree of alignment. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Phospholipid Bilayer Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Mosaic of proteins float in fluid lipid bilayer. Fluid Mosaic Model Mosaic of proteins float in fluid lipid bilayer. Transmembrane Proteins Network of Supporting Fibers Exterior Proteins and Glycolipids Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Cell Membrane Proteins Six Major Classes Transporters-allow certain substances to enter or leave the cell (channels or carriers) Enzymes-catalyze reactions Cell Surface Receptors-act like antennae to pick up chemical messages Cell Surface Identity Markers-allow other cells to identify them (immune system) Cell Adhesion Proteins-allows cells to glue themselves to other cells Cytoskeleton Attachments-allow surface proteins to be anchored to the cytoskeleton within the cell Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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Continues until equilibrium reached. Diffusion Random motion causing net movement of substances from regions of high concentration to regions of lower concentration. Continues until equilibrium reached. Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Facilitated Diffusion Each polar molecule transported across the plasma membrane has its own type of channel. Selective permeability Ions move across membrane in ion channels. Direction of movement determined by relative concentrations and voltage across membrane. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Facilitated Diffusion Carriers facilitate movement of solutes across membrane by physically binding to them on one side of the membrane and releasing them on the other. Driven by concentration gradients. Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Most solutes are not lipid soluble and thus cannot cross membrane. Osmosis In an aqueous solution, both water and solutes diffuse down a concentration gradient. Most solutes are not lipid soluble and thus cannot cross membrane. Water flows through aquaporins (special water channels) in membrane. Net movement of water across a membrane is termed osmosis. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Osmotic Concentration - Concentration of all solutes in a solution. Osmosis Osmotic Concentration - Concentration of all solutes in a solution. Hyperosmotic (hypertonic)- Solution with higher concentration. Hypoosmotic (hypotonic)- Solution with lower concentration. Isosmotic (isotonic)- Osmotic concentrations of both solutions are the same. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Osmosis Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Mechanisms For Maintaining Osmotic Balance Extrusion Osmotic Pressure Hydrostatic Pressure is caused by cytoplasm pushing out against cell membrane. Osmotic Pressure is the pressure necessary to stop osmotic movement of water across a membrane. Mechanisms For Maintaining Osmotic Balance Extrusion Isosmotic Solutions Turgor Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Phagocytosis - Particulate form. Pinocytosis - Liquid form. Bulk Passage Endocytosis - Plasma membrane extends outward and envelops food particles. Phagocytosis - Particulate form. Pinocytosis - Liquid form. Receptor-Mediated Endocytosis - Molecules first bind to specific receptors on plasma membrane. Excoytosis - Discharge of material from vesicles at cell surface. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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Exocytosis Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Requires input of energy. Active Transport Moving substances across a membrane against their concentration gradients. Requires input of energy. Enables cell to take up additional molecules of a substance already present in its cytoplasm in concentrations higher than in extracellular fluid. Sodium-Potassium Pump Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Establish the down gradient. Sodium-potassium or proton pump. Coupled Transport Active transport that moves molecules with sodium ions or protons moving down their concentration gradients (Cotransport). Establish the down gradient. Sodium-potassium or proton pump. The concentration gradient that is produced by pumping Na+ out can be used to move large molecules inside. Example: The potential energy of Na+ gradient helps move sugar inside the cell. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies